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216 THE CARBOHYDRATES.
This reaction depends, according to Ville and Derrien, as well as to
V. Ekenstein and Blanksma 1
upon the formation of oxymethylfurfurol
which reacts with the a-naphthol. As oxymethylfurfurol is formed from
all hexoses, hence Molisch’s reaction is a general reaction for hexoses.
Diazobenzenesulphonic acid gives with a glucose solution made alkaline
with a fixed alkali a red color, which after 10-15 minutes gradually changes to
violet. Orthonitrophenylpropiolic acid yields indigo when boiled with a
small quantity of glucose and sodium carbonate, and this is converted into
indigo-white by an excess of sugar. An alkaline solution of glucose is colored
deep red on being warmed with a dilute solution of picric acid. The behavior
of glucose toward certain pentose reactions has been given on page 209.
A more complete description as to the performance of these several
tests will be given in detail in a subsequent chapter (on the urine).
Glucose is prepared, pure, by inverting cane-sugar by the follow-
ing simple method of Soxhlet and Tollens, which is a modification of
Schwarz’s 2
method:
Treat 12 liters 90 per cent alcohol with 480 cc. fuming hydrochloric
acid and warm to 45-50° C; gradually add 4 kilos of powdered cane-
sugar, and allow to cool after two hours, when all the sugar will have
dissolved and been inverted. To incite crystallization, some crystals of
anhydrous glucose are added, and after several days the crystals are
sucked dry by the air-pump, washed with dilute alcohol to remove
hydrochloric acid, and crystallized from alcohol or methyl alcohol.
According to Tollens it is best to dissolve the sugar in one-half its
weight of water on the water-bath and then add double this volume of
90-95 per cent alcohol.
In detecting glucose in animal fluids or extracts of tissues we may
make use of the above-mentioned reduction tests, the optieal deter-
mination, fermentation, and phenylhydrazine tests. For the quantitative
estimation the reader is referred to the chapter on the urine. Those
liquids containing proteins must first have these removed by coagulation
with heat and addition of acetic acid, or by precipitation with alcohoL
or metallic salts, before testing for glucose. In regard to the difficulties
of operating with blood and serous fluids we refer the student to larger
works.
Mannoses. d-Mannose, also called seminose, is obtained with d-fructose on
the careful oxidation of d-mannite. It is also obtained on the hydrolysis of
natural carbohydrates, such as salep slime and reserve cellulose (especially
from the shavings of the ivory-nut). It is dextrorotatory, readily ferments,
with beer-yeast, gives a hydrazone not readily soluble in water, and an osazone
which is identical with that from d-glucose.
d-Galactose (not to be mistaken for lactose or milk-sugar) is obtained on
the hydrolytic cleavage of milk-sugar, and by the hydrolysis of many other
1
Bull. soc. chim. (4), 5, 895 (1909); Ber. d. d. ohem. Gesellsch., 43, 2358 (1910).
2
Tollens, Handbuch der Kohlehydrate, 2. Aufl. I, 39.
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